A fine-grinding machine is known from German Pat. No. 868,410 issued Jan. 15, 1953 to Karl Krummel. This device is adapted to be mounted on the tool post of a lathe for mirror finishing a shaft. It has an electric motor which rotates a tube shaft inside of which is provided a shaft carrying an eccentric. The angular position of the central shaft and outer tube shaft can be changed to vary the extent of eccentricity of the eccentric carried by the central shaft. This eccentric rides in a bearing in turn riding in a slot in a tool mount that is reciprocal in a direction perpendicular to this slot. Thus, as the motor rotates the tube and central shafts, the eccentric will orbit about the axis of the tube shaft and will reciprocate the tool mount in its guide. As the degree of eccentricity of the eccentric is increased relative to the tube-shaft axis the diametrical stroke of the tool mount will increase, and vice versa.
This apparatus has shown itself relatively useful in the limited application to which it is intended, that is mirror-finishing the exterior of a shaft or the like. In view of the considerable complexity of the structure of even this simple device it has been considered impossible to overcome its lack of versatility to use it for other finishing jobs.
U.S. Pat. No. 3,959,929 issued June 1, 1976 to Johann Fleischmann et al shows another such arrangement wherein the grinding device is mounted on an arm of a tool stand. The tool itself in this arrangement is rotatable about a vertical axis and can simultaneously be reciprocated vertically. In order to be able to machine surfaces that are not perfectly horizontal relative to the workpiece, the entire machining arrangement can be tipped on the arm, in the fashion of a raidal-arm drill press or saw, to have a different angle of attack. The workpiece is normally mounted with two degrees of freedom of motion, that is for at least limited free displacement in a plane. Such a tool cannot, however, machine horizontal upper surfaces of a workpiece.
A disadvantage of the known machine is the inability to finish recesses produced by electro-discharge machining (EDM). It is known to use a diamond paste or similar abrasive agents between the EDM tool and the workpiece. Such arrangements, however, normally require that not only the base of the recess be finished, but also the sides thereof. This normally requires a special-duty machine or two separate machines.